1. Field of the Invention
This invention relates to a photo detector used for visible ray sensors or infrared ray sensors controlling operations of various apparatuses or measuring environmental data.
2. Prior Art
This kind of conventional photo detector is disclosed in Unexamined Japanese Patent Application No. 52-42390 published in 1977, or in Unexamined Japanese Patent Application No. 6-122461 published in 1994.
FIG. 14 shows a conventional photo detector. A pair of leads 101 are assembled with a ceramic case 102. An epoxy-group resin portion 103 is provided in the ceramic case 102. A predetermined amount of dye 104 is added to this epoxy-group resin portion 103. With this additive, the maximum value of the spectral sensitivity of a semiconductor light-receiving element 105 is shifted from 650 nm to 570 nm in wavelength as shown in FIG. 15. Wavelength 650 is closer to the maximum visible sensitivity. Thus, the visible sensitivity can be optimized.
According to another conventional photo detector, a plurality of plates (not shown) different in their light transmittance are prepared. Among these plural plates, an optimum plate is combined with a photo semiconductor element to compensate a dispersion caused in the spectral sensitivity characteristics of this photo sensitive element. Thus, the photoelectric current output of the photo detector can be stabilized.
According to still another photo detector, a photo semiconductor element detects an incident light quantity by using the entirety of its wavelength sensitive range.
On the other hand, another photo detector detects an incident light quantity by cutting some components of particular wavelengths.
For example, a solar-radiation sensor is used in an automotive air-conditioning system. To detect any change in the thermal energy derived from solar radiation, a semiconductor element used in this solar-radiation sensor has a wavelength sensitivity ranging from 400 nm to 1,200 nm as characterized by a spectral sensitivity shown in FIG. 12.
This solar-radiation sensor has an incident light window permitting light to enter through a glass. A visible ray cutting agent is used to cut some components of light having wavelengths in the range of 400 nm to 700 nm. By the adoption of this visible ray cutting agent, the solar-radiation sensor can detect a solar-radiation quantity corresponding to the light components having wavelengths in the range of 700 nm to 1,200 nm. An output signal of the solar-radiation sensor is sent to a controller of the automotive air-conditioning system that controls the temperature in a compartment of an automotive vehicle automatically.
Furthermore, a light sensor is used in an automatic lighting system. To detect any change of surrounding brightness, a semiconductor element used in this light sensor has a wavelength sensitivity ranging from 400 nm to 1,200 nm as characterized by a spectral sensitivity shown in FIG. 13. The light sensor detects a light quality corresponding to all the light components whose wavelengths are within the entire range of 400 nm to 1,200 nm. An output signal of the light sensor is sent to a controller of the automatic lighting system that turns on and off the lights of an automotive vehicle automatically in accordance with surrounding brightness (i.e., in response to daylight and dark).
In this manner, for automotive vehicles, two different sensors are used for both the air-conditioning system and the automatic lighting system.
Using the above-described solar-radiation sensor as a light sensor is not preferable, because the photo semiconductor element having the spectral sensitivity shown in FIG. 12 has a strong sensitivity to an infrared ray. As a recent advanced optical system, there is a plate number recognition system for optically reading a plate number of a vehicle passing nearby. This type of recognition system emits an infrared ray with a peak of 900 nm, for example. When a vehicle with the above sensor passes by this kind of recognition system in the dark, the sensor possibly reacts against the infrared ray and the vehicle lights will be suddenly turned off.
From the foregoing reasons, it was impossible to use a single solar-radiation sensor for both of the automotive air-conditioning system and the automatic lighting system.
Furthermore, changing the spectral sensitivity of a photosensor is not easy. This requirement possibly causes a change of wafer material or forces to change the manufacturing processes. In other words, manufactured parts will be special products rather than standard products. This will lead to an increase of costs.